Growing seedlings in cold frames and plastic tunnels
Enjoy an early harvest of seasonal vegetables as well as prepare your garden for stunning displays of annual flowers by protecting young plants and seedlings in a cold frame or growing tunnel.
How do Cold frames work?
A cold frame is a smaller version of a green house. They collect solar heat, keeping temperatures warm at night, thus protecting from frost or damage from cold weather. Where some gardens are not large enough for a structure like a green house the problem can be solved by using a cold frame.
Placed directly over plants in the place where the plants will stay positioned right through the season or with a base on the frame for seedlings in trays.
What is a cold frame?
A cold frame is generally made from wooden, plastic or lightweight metal sides, creating a frame with an adjustable glass or clear polythene lid. Preferably attach the lid on a slanted angle to allow moisture drainage, with a hinge for ease of opening.
When to use a cold frame / growing tunnel?
With vegetable crops cold frames allow vegetable growers to plant for early crops in late winter/early spring to get the jump on the season, also where colder climate vegetables can be started in autumn and grown right through the winter under cold frames.
Likewise with ornamental annuals the same theory applies, start seedlings in late winter/ early spring and produce early growing strong, hardened off seedlings.
The cold frame is perfect for hardening off seedlings allowing the plants to adjust to a colder climate before being subject to the full elements.
Tips for use of a cold frame or growing tunnel.
- When temperatures are expected to reach below zero cover the entire cold frame or tunnel with a plastic sheet or tarpaulin and insulate the outer sides with mulch or straw.
- When seedlings reach a size almost ready to plant out open the cold frame or ends of growing tunnel for longer periods each day, still closing it at night. This will help adjust your seedlings ready for planting out.
- When sun gets stronger be sure to lift lids or open ends of tunnel slightly to allow air flow and excess moisture to escape.
- To prevent plants from getting leggy and growing too tall too fast paint the inside of the cold frame white to reflect light more evenly and reduce stretching. Most plastic growing tunnels donÂ’t require this treatment as the light penetration is more even.
- When preparing winter vegetable crops propagate seeds indoors in late summer and place them in cold frames in early autumn so they have time to harden up to the colder elements and are ready for planting out.
- Get the jump on early spring vegetables and spring/summer annuals by introducing the seedlings to cold frames during the last weeks of winter.
